Low floor vehicle ramp assembly

ABSTRACT

A ramp assembly ( 20 ) for mounting in a low floor bus ( 22 ) or other vehicle. The ramp assembly ( 20 ) includes a rectangular enclosure ( 24 ) that fits underneath the chassis of the low floor bus ( 22 ). The ramp assembly ( 20 ) includes a reciprocating mechanism ( 26 ) for moving a ramp platform ( 28 ) between a fully deployed position and a fully stowed position. During this movement, the reciprocating mechanism ( 26 ) raises the trailing end of the ramp platform ( 28 ) in one translational movement with the extension of the ramp platform, such that the trailing end of the ramp platform, when deployed, is raised to the floor level of the low floor bus ( 22 ).

REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 09/164,434,filed Sep. 30, 1998, abandoned, which is a continuation-in-part of U.S.patent application Ser. No. 09/060,948, filed Apr. 15, 1998, now U.S.Pat. No. 6,186,783, both of which are incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

This invention relates generally to retractable ramp platforms thatfacilitate boarding of a passenger onto a vehicle and, in particular,retractable ramp platforms that facilitate access to a low floorvehicle.

BACKGROUND OF THE INVENTION

Intra-city buses have included wheelchair lifts for transporting personsof limited mobility in and out of the vehicles. Typically, a prior artwheelchair lift included a mechanically driven platform to raise andlower a passenger between loading from outside of the vehicle at groundlevel and entry into the vehicle at a vehicle floor level. For example,wheelchair lifts of the type installed in the stairwell of transitvehicles, such as intra-city buses, have been used for some time. Onetype of prior art wheelchair lift, commonly referred to as a “step lift”was disclosed in U.S. Pat. No. 4,466,771 to Thorley et al. The step liftin Thorley et al. was designed to be installed in the stairwell of atransit vehicle, and included hinged panels that were movable between astep configuration and a platform configuration. In the stepconfiguration, the hinged panels formed steps for use by passengers toboard and exit the vehicle. In the platform configuration, the hingedpanels formed a horizontal platform used to raise and lower a wheelchairpassenger between a vehicle floor-level position and a ground-levelposition.

Municipalities recently began using “low floor buses.” In this style ofbus, a passenger entered the bus at a level that was above ground by asufficient amount so that the chassis had proper ground clearance. Thefloor of the bus throughout the vehicle was substantially at this level.It was believed that such buses were more stable in operation, andpermitted simpler egress and ingress of passengers.

A problem encountered with the low floor buses was that wheelchair liftssuch as were disclosed in Thorley et al. could not be installed in thebuses because there was not a stairwell. Moreover, the low floor buseslacked sufficient under-chassis space to mount the complex liftingmechanisms for a wheelchair lift. Therefore, other systems had to bedeveloped to accommodate wheelchair users and other passengers oflimited mobility. To address these concerns, some manufacturersdeveloped ramp assemblies for providing limited mobility passengersaccess into and out of the low floor buses. The ramp assemblies werestructures that selectively provided a ramp platform that extendedbetween the outside ground and the floor of a vehicle such as anintra-city bus to provide access into and out of the vehicle.

Prior art ramp assemblies typically stowed the ramp platform under thevehicles when not in use, and deployed the ramp platform when it wasnecessary to provide passenger access. When the ramp platform wasdeployed, the two ends were positioned at different heights, creating aslope upward from the ground to the bus floor. An example of a rampassembly for use in a low floor bus was disclosed in U.S. Pat. No.5,636,399 to Tremblay et al. A similar ramp assembly for use in a vanwas disclosed in U.S. Pat. No. 5,393,192 to Hall et al.

One of the problems found in designing prior art ramp assemblies for lowfloor vehicles was the limited amount of space allotted for the rampplatform and its reciprocating mechanism, including the motor andnecessary drive mechanism. Because the low floor buses lacked astairwell and a raised floor under which the ramp assembly could bemounted, the designer was forced to minimize size in all dimensions toprevent loss of ground clearance or interference with otherunder-chassis structures. Tremblay et al. and Hall et al. addressed thisproblem by providing a compact ramp assembly. However, while the rampassemblies disclosed in Tremblay et al. and Hall et al. were relativelysmall, the motors used for the ramps were mounted behind or underneaththe frame for the ramp assembly, requiring additional installation areaunderneath the vehicle. There exists a need for a more efficient mannerof mounting a motor for a ramp assembly.

Another problem with the prior art ramp assemblies was that the rampplatform was stowed several inches below the floor level and, to reachthe deployed position, had to be raised to extend between the floor andthe ground. Alternatively, some form of transition between the ramp inthe deployed position and the floor had to be provided. Tremblay et al.addressed this problem by providing a hinged panel that formed atransition between the floor and the ramp platform. Hall et al., on theother hand, provided a complex tilting mechanism utilizing areciprocating motor to lift the trailing end of the ramp to floor level.There is a need for a less complex mechanism for providing a transitionbetween the floor and a ramp platform.

Another problem with prior art ramp assemblies is that, if power was cutto the reciprocating mechanism for the ramp platform, the ramp platformmay be stuck in a deployed position. In such case, the driver of the buswould have to wait for maintenance crews to repair, or at least stow,the ramp platform. There is a need for a more simple way of retracting aramp platform when the reciprocating mechanism for the ramp platform isinoperable.

SUMMARY OF THE INVENTION

The present invention solves many of the above problems by providing anovel ramp assembly for mounting on a vehicle. In accordance with oneembodiment of the invention, the ramp assembly includes a frame formounting below a floor of a vehicle and a ramp platform mounted in theframe. A reciprocating mechanism is provided for extending andretracting the ramp platform along a length of the frame between stowedand deployed positions. The ramp platform is stowed substantially alonga plane, and is arranged when deployed such that the forward end of theramp platform extends down toward the ground. The ramp platform includesmeans connected to the reciprocating mechanism for raising the trailingend of the ramp platform in one translational movement with theextension of the ramp platform, such that the trailing end of the rampplatform, when deployed, is raised above the plane.

In one embodiment, the means for raising includes a lever having adistal end attached to the trailing end of the ramp platform and asecond end rotatably attached to the reciprocating mechanism. The leveris configured to rotate about the second end as the reciprocatingmechanism is extended, thereby lifting the trailing end upward.

In a preferred embodiment, the frame includes an abutment surface thatis engaged by the lever when the ramp platform is extended, theengagement of the abutment surface by the lever causing the lever torotate. The abutment surface is preferably a pin, which is engaged by aslot on the lever when the ramp platform is extended. The slot ispreferably curved, such that the curved slot causes a smoothtranslational lifting movement of the trailing end.

In accordance with one aspect of the invention, the frame includes a camslot and the lever includes a cam follower, the cam slot and the camfollower being configured such that during extension of the rampplatform, the cam follower follows the cam slot and the lever engagesthe pin and the cam follower continues forward such that the lever isrotated to lift the trailing end of the ramp platform.

In accordance with another aspect of the invention, the reciprocatingmechanism includes a motor. The motor is mounted for reciprocatingmovement with the ramp platform.

In yet another embodiment, a rod extends the length of the frame, and apower cord for supplying power to the motor is coiled around the rod andis attached at one end to the frame and at another end to thereciprocating mechanism.

In accordance with other aspects of the invention, a first lockingmechanism is provided that locks the ramp platform into a fully deployedposition, and a second locking mechanism is provided that locks the rampplatform into a fully stowed position. Actuation of a single manualrelease mechanism releases the first locking mechanism when the rampassembly is in the fully deployed position and releases the secondlocking mechanism when the ramp platform is in the fully stowedposition.

The first locking mechanism preferably includes a first latch armoperatively associated with the reciprocating mechanism to extend andretract with the ramp platform and a first latch plate attached to theframe that is engaged by the first latch arm when the ramp platform isin the fully deployed position. A second latch arm can be operativelyassociated with the reciprocating mechanism to extend and retract withthe ramp platform that engages a second latch plate attached to theframe when the ramp platform is in the fully deployed position. Thefirst locking mechanism is further associated with the second lockingmechanism by means of a coupling arm, causing both first and secondlocking mechanisms to operate substantially simultaneously whenactuated. The second locking mechanism preferably includes a third latchplate attached to the frame that is engaged by the second latch arm whenthe ramp platform is in the fully stowed position.

The single manual release mechanism preferably includes a handle (1)operatively associated with the first latch arm when the ramp platformis in the deployed position such that actuation of the handle causesboth the first and second latch arms to release the first and secondlatch plates, and (2) operatively associated with the second latch armwhen the ramp platform is in the stowed position such that actuation ofthe handle causes the second latch arm to release the third latch plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a partial side view of a low floor bus having a ramp assemblymade in accordance with the present invention;

FIG. 2 is a front isometric view of the ramp assembly in FIG. 1, withthe ramp assembly removed from the low floor bus, the ramp platformfully deployed, and the top panel removed for detail;

FIG. 3 is a front isometric view of the ramp assembly in FIG. 2, withthe ramp platform fully stowed;

FIG. 4 is a rear isometric view of the ramp assembly in FIG. 2;

FIG. 5 is a top plan view of the ramp assembly in FIG. 2;

FIG. 6 is a sectional view of the rectangular enclosure for the rampassembly in FIG. 1, taken along the sectional lines 6—6 in FIG. 5, withthe rectangular motor plate and the ramp platform removed for detail;

FIG. 7 is a partial sectional view taken along the sectional lines 7—7in FIG. 5;

FIG. 8 is a partial sectional view taken along the section lines 6—6 inFIG. 5, with the rectangular motor plate and the ramp platform inposition;

FIG. 9 is a sectional view similar to FIG. 6, with the rectangular motorplate and the ramp platform in position, and the ramp platform fullystowed;

FIG. 10 is a partial sectional view similar to FIG. 8, with the rampplatform 14 inches retracted;

FIG. 11 is a partial sectional view similar to FIG. 8, with the rampplatform 11 inches retracted;

FIG. 12 is a partial sectional view similar to FIG. 8, with the rampplatform 9 inches retracted;

FIG. 13 is a partial sectional view similar to FIG. 8, with the rampplatform 6 inches retracted;

FIG. 14 is a partial sectional view similar to FIG. 8, with the rampplatform 4 inches retracted;

FIG. 15 is a partial sectional view similar to FIG. 8, with the rampplatform 1¼ inch retracted;

FIG. 16 is a partial sectional view similar to FIG. 8, with the rampplatform ¾ inch retracted;

FIG. 17 is a partial sectional view similar to FIG. 8, with the rampplatform 1½ inch retracted;

FIG. 18 is a partial sectional view similar to FIG. 8, with the rampplatform ¼ inch retracted;

FIG. 19 is a top plan view of the ramp assembly in FIG. 2, showing thelatching mechanism of the present invention, with the rectangular motorplate and the ramp platform removed for detail, and the ramp assembly inthe deployed position;

FIG. 20 is a detail view of the first latch plate of the latchingmechanism in FIG. 19, with the latch pivot arms and the coupling armremoved for detail;

FIG. 21 is a detail view of the first latch plate in FIG. 20, with thelatch arm manually actuated;

FIG. 22 is a detail view of the second latch plate of the latchingmechanism in FIG. 19 with the latch pivot arms and the coupling armremoved for detail;

FIG. 23 is a detail view of the second latch plate in FIG. 20, with thelatch arm manually actuated;

FIG. 24 is a top plan view similar to FIG. 19, with the ramp assembly inthe stowed position;

FIG. 25 is a detail view of the first latch arm in FIG. 24;

FIG. 26 is a detail view of the first latch arm in FIG. 25, with thelatch arm manually actuated;

FIG. 27 is a detail view of the second latch arm in FIG. 24;

FIG. 28 is a detail view of the second latch arm in FIG. 25, with thelatch arm manually actuated;

FIG. 29 is a rear, top perspective view of a second embodiment of a rampassembly made in accordance with the present invention, with the rampplatform in the deployed position;

FIG. 30 is a front, top perspective view of the ramp assembly in FIG.29, with the ramp platform in the stowed position;

FIG. 31 is a top cutaway view of the rectangular motor plate for theramp assembly in FIG. 29;

FIG. 32 is a side cutaway view of the lever arm of the ramp assembly inFIG. 29, with the ramp platform deployed a distance that issubstantially the same as the deployment of the ramp platform in FIG.15;

FIG. 33 is an exploded perspective view of the attachment of the leverarm in FIG. 32 to the ramp platform;

FIG. 34 is an operation diagram for a delay circuit for the solenoidsand motor of the ramp assembly in FIG. 29;

FIG. 35 is a bottom cutaway view of an adjustable deployed latch platefor the ramp assembly in FIG. 29;

FIG. 36 is a bottom view of the adjustable deployed latch plate in FIG.35, with the bottom plate removed, and a latch arm shown in positionagainst the latch plate;

FIG. 37 is a rear, underside view of a belt release mechanism for theramp assembly in FIG. 29,

FIG. 38 is the belt release mechanism in FIG. 37, with the rectangularenclosure for the ramp assembly removed for detail;

FIG. 39 is a side perspective view of the belt release assembly for thebelt release mechanism in FIG. 38;

FIG. 40 is a front, top perspective view of the ramp assembly in FIG.29, with the belt release mechanism released so that the tension in thebelt is removed;

FIG. 41 is a detailed cutaway view of the handles for the belt releasemechanism and manual unlatching mechanism of the ramp assembly in FIG.29, with the handle for the belt release mechanism turned to a lockedposition;

FIG. 42 is the belt release mechanism in FIG. 38, with the beltreleased;

FIG. 43 is the belt release assembly in FIG. 39, with the belt releasemechanism in the position shown in FIG. 42;

FIG. 44 is a side perspective view of a drive belt clutch mechanism inthe ramp assembly in FIG. 29;

FIG. 45 is a side perspective view of a clutch saddle in the drive beltclutch mechanism in FIG. 44;

FIG. 46 is a side cutaway view showing the drive belt extending throughthe drive belt clutch mechanism in FIG. 44, with the drive belttensioned;

FIG. 47 is the cutaway view in FIG. 46, with the drive belt released;

FIG. 48 is a side perspective view of an adjustable clamp for a belttensioner in the ramp assembly in FIG. 29;

FIG. 49 is a stationary plate used with the adjustable clamp in FIG. 48in formation of the belt tensioner for the ramp assembly in FIG. 29;

FIG. 50 is a release tool for use with the ramp assembly in FIG. 29;

FIG. 51 is a rear, bottom perspective view of the ramp assembly in FIG.29;

FIG. 52 is a side cutaway view of the belt tensioner for the rampassembly in FIG. 29, the parts of which are shown in FIGS. 40 and 49;and

FIG. 53 is a side perspective view of a wire rope retainer for thepulleys in the ramp assembly in FIG. 29.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawing, in which like reference numerals representlike parts throughout the several views, FIG. 2 shows a ramp assembly 20for mounting in a low floor bus 22 (FIG. 1) or other vehicle. The rampassembly 20 fits within a frame, in the drawings shown as a rectangularenclosure 24, that fits underneath the chassis of the low floor bus 22.The ramp assembly 20 includes a reciprocating mechanism 26 for moving aramp platform 28 between a fully deployed position (FIG. 2) and a fullystowed position (FIG. 3).

The rectangular enclosure 24 includes side panels 32, 34, an end panel36, a bottom panel 38 and a removable top panel 40 (shown removed fromand raised above the rectangular enclosure 24 in FIG. 3). The sidepanels 32, 34, the end panel 36, and the bottom panel 38 are a weldmentthat provides a structural frame to house the ramp platform 28 and thereciprocating mechanism 26 along the plane of the rectangular enclosure24. Preferably, the side panels 32, 34 include bottom flanges (notshown) that provide structural support for the bottom panel 38. The toppanel 40 functions as a cover for the rectangular enclosure 24 and, asdescribed above, is removable. The rectangular enclosure 24 is attachedbelow the doorway of the low floor bus 22 by brackets 41, welding oranother method known in the art. When in place, the top panel 40 islocated just below the floor of the doorway of the low floor bus 22(FIG. 1).

A hinged closure panel 42 (FIG. 3) is attached to the forward end of therectangular enclosure 24 (opposite the end panel 36). The hinged closurepanel 42 is hinged from the bottom panel 38 and is spring-loaded to theclosed position. The hinged closure panel 42 includes V-shaped brackets44 (FIG. 8) on its inner side, adjacent to the side panels 32, 34, andarranged so that the point of the V extends toward the end panel 36 whenthe hinged closure panel 42 is closed. As is described in detail below,the V-shaped brackets 44 are contacted by the ramp platform 28 at thebeginning of deployment of the ramp platform so as to open the hingedclosure panel 42.

FIG. 6 shows a side view of the inside of one of the side panels 34. Theside panel 34 includes a guide bar 46 extending along an upper surfacethereof. The outboard, or forward end of the guide bar 46 has aserpentine profile. Specifically, the guide bar 46 extends upward at arear juncture 48 and continues upward to a peak 50 where the guide barturns and extends downward to a forward juncture 52. Just forward of theforward juncture 52, the guide bar 46 tapers upward at a sloped frontedge 53.

The outer edges of the bottom panel 38 include bottom flange supportbearings 54 directly below the guide bars 46. The bottom flange supportbearings 54 can rest on top of bottom flanges for the side panels 32,34, if provided. The bottom flange support bearings 54 extend along thebottom panel 38 adjacent to the side panel 34 and underneath the guidebars 46, and are preferably manufactured from a low friction materialsuch as Nylatron™ bearing material. The bearing material does notrequire lubrication, which improves reliability and reduces maintenance.The bottom flange support bearings 54 are preferably the same heightalong their lengths, with the exception of a tapered leading edge 55(FIG. 6).

Cap screw heads, or pins 56 (FIG. 6), extend into the side panels 32,34, and are located at the forward end of the rectangular enclosure 24just above the forward juncture 52 of the guide bars 46. As described indetail below, the pins 56 act as abutment surfaces for rotating thetrailing end of the ramp platform upward at the end of deployment of theramp platform.

An upper cross-member 58 spans the width of the forward end of therectangular enclosure 24. The upper cross-member 58 provides additionalstructural support for the rectangular enclosure 24, as well asthreshold support for passenger foot traffic at the edge of the doorwayfor the low floor bus 22.

A structural channel 60 (FIG. 2) is located above the reciprocatingmechanism 26 and the ramp platform 28, and is fixed between the rearwardportion of the rectangular enclosure 24 (adjacent to the end panel 36)and the upper cross-member 58. The structural channel 60 provideslongitudinal structure for the rectangular enclosure 24, as well assupport for components of the reciprocating mechanism 26, as isdescribed in detail below.

The reciprocating mechanism 26 includes a rectangular motor plate 62having bearing strips 64 attached at its ends. The rectangular motorplate 62 is of sufficient length so as to rest on top of and run alongthe bottom flange support bearings 54 on opposite sides of the bottompanel 38. The bearing strips 64 are of sufficient height and shape tofit snugly between the guide bars 46, the rectangular motor plate 62,and the bottom flange support bearings 54. The bearing strips 64 arepreferably manufactured from a low-friction material so that they freelyslide along the top of the bottom flange support bearings 54 and bottomsurface of the guide bars 46.

An electric motor 72 is attached to a motor mount 77, which is mountedon the rectangular motor plate 62 such that the motor extends lengthwiseon the motor plate and such that a motor shaft (not shown) extending outof the electrical motor also extends lengthwise. A flexible coupling 74b connects the motor shaft to a drive shaft 74 a (FIG. 5). Although theelectric motor 72 is disclosed as being electric, it is to be understoodthat hydraulic, pneumatic, or other powered motors could be used. Adrive pulley 76 (FIG. 7) is located on the drive shaft 74 a. The driveshaft 74 a is supported by bearings (not shown) pressed into a mountingplate 73 (FIG. 7) that is attached to the rectangular motor plate 62.

A pair of idler pulleys 78 (FIG. 7) are mounted on opposite sides of thedrive pulley 76. The central axes of the idler pulleys 78 extendparallel to the central axis of the drive pulley 76. The idler pulleys78 roll on stationary idler shafts 78 a, using bearings (not shown).

A drive belt 80 is fixed at both ends to opposite ends of therectangular enclosure 24. The drive belt 80 includes ribs or holes (notshown) that are engaged by teeth 81 on the drive pulley 76 (FIG. 7). Thedrive belt 80 extends over both of the idler pulleys 78 and under thedrive pulley 76, ensuring proper engagement of the drive belt 80 withthe drive pulley 76. The forward end of the drive belt 80 is attached bya drive belt clamp 79 that is adjustable to tension the drive belt 80.The structural channel 60 provides support for the drive belt clamp 79,and serves as a cover for the drive belt 80.

A torque shaft 82 (FIG. 3) extends along the forward edge of therectangular motor plate 62 and is mounted for rotation in bores 64 a inthe forward end of the bearing strips 64. Lever arms 84 (FIG. 8) aremounted on opposite ends of the torque shaft 82 for rotation with thetorque shaft. Each of the lever arms 84 is shaped like an elongatetriangle with rounded edges. The pointed distal end of the elongatetriangle faces forward, and the bottom opposite corner of the triangleis attached for rotation on the torque shaft 82. A curved slot 86 islocated on the third comer of the triangle and faces upward. Thetriangular shape of the lever arm 84 causes the mouth of the curved slot86 to face somewhat forward as well as upward. The pointed, forward endof each of the lever arms 84 is pivotally attached to trunnions 87 thatare fixed to the sides of the ramp platform 28 near its rearward end(FIG. 4).

Each of the trunnions 87 includes a circular bearing 88 mounted thereonand attached to the associated lever arm 84. The circular bearing 88functions as a cam follower located between and influenced by the guidebars 46 and the bottom bearing flange support 54.

A coiled electrical cable 90 (FIGS. 3 and 5 only) supplies power to theelectrical motor 72 and other electrical components on the rectangularmotor plate 62. The coiled electrical cable 90 wraps around a rod 92that extends the length of the upper portion of the rectangularenclosure 24. The coiled electrical cable 90 is configured much like anextension spring, such that as the rectangular motor plate 62 travelsback and forth through its range of motion, the coiled electrical cablecompresses in the stowed position (FIG. 3), and stretches the length ofthe rectangular enclosure 24 in the deployed position (FIG. 5). Duringthis extension and retraction, the coiled electrical cable 90 issupported and guided by the rod 92, which prevents the coiled electricalcable from becoming entangled in the reciprocating mechanism 26. Ifdifferent types of motors are used, power (such as hydraulic fluid) canbe supplied by a similar coiled supply line.

The ramp platform 28 is rectangular in shape and is of sufficient widthto accommodate persons in wheelchairs and/or mobility aid devices. Tominimize weight, the ramp platform 28 is preferably constructed of thinsheet metal having a corrugated sheet 102 (FIG. 10) extending betweenupper and lower sheets 104, 106. Alternatively, the ramp platform can bemade of lightweight aluminum or a composite material of sufficientstrength and stiffness to support the weight of passengers boarding theramp platform 28. A non-skid material or other covering (not shown) canbe used on the top surface of the ramp platform 28 to aid a passenger inloading the vehicle.

Stationary side curbs 108 extend along the outer edges of the rampplatform 28. The stationary side curbs 108 are preferably at least twoinches in height, thereby preventing a wheelchair or a mobility aiddevice from rolling off of the sides of the ramp platform 28. Therearward, or inboard ends of the stationary side curbs 108 includebevels 110, which permit deployment of the ramp platform 28 withoutinterference with the enclosure 24.

The ramp platform 28 includes a beveled leading edge 114 extending alongthe width of its forward end. The beveled leading edge 114 contacts theground when the ramp platform 28 is fully deployed so as to provide aminimum threshold height when the wheels of a wheelchair roll onto theramp platform.

Bearing blocks 116 are attached to the leading outside edges of thestationary side curbs 108. The bearing blocks 116 extend between theguide bars 46 and the bottom flange support bearings 54 when the rampplatform 28 is withdrawn to the stowed position. The bearing blocks 116prevent the ramp platform 28 from rattling or bouncing within theenclosure as the vehicle travels down roadways.

A latch mechanism 120 (FIGS. 19-28) is used to selectively hold the rampplatform 28 in the deployed or stowed positions. The latch mechanism 120includes first and second latch arms 122, 124 (best shown in FIGS. 20AND 22) extending underneath the rectangular motor plate 62 andpivotally mounted about their centers on pins 126, 128. The pins 126,128 extend through orthogonal bores (not shown) in the left central andright central halves of the rectangular motor plate 62, respectively.Thus, the first and second latch arms 122, 124 travel with therectangular motor plate 62 during extension and retraction of the rampplatform 28.

The first latch arm 122 includes a cutout 130 on the front, right end ofthe latch arm. The cutout 130 is spaced from the pin 126. The secondlatch arm 124 includes two cutouts 132, 134 located on opposite sidesand on opposite ends of the second latch arm. Both of these cutouts 132,134 are spaced from the pin 128.

Movement of the two latch arms 122, 124 is tied by a coupling arm 136, ashort pivot arm 138, and a long pivot arm 140. The short pivot arm 138is attached for rotation with the first latch arm 122 by the pin 126,and extends above the rectangular motor plate 62 parallel with therearward portion of the first lever arm 122. The long pivot arm 140 isfixed for rotation with the second latch arm 124 by the pivot pin 128,and extends above the rectangular motor plate 62 parallel with thesecond latch arm 124. The coupling arm 136 is rotatably attached to thedistal, rearward ends of the short pivot arm 138 and long pivot arm 140.The opposite end of the long pivot arm 140 is attached to the apex of atriangular plate 142. The base of the triangular plate 142 is attachedto the actuating arms on a pair of solenoids 144.

Actuation of the solenoids 144 causes the long pivot arm 140 to rotate,which through the coupling arm 136 causes the short pivot arm 138 torotate. Because the short pivot arm 138 is fixed for rotation with thelatch arm 122, and the long pivot arm 140 is fixed for rotation with thelatch arm 124, rotation of the short and long pivot arms 138, 140 causesa corresponding rotation of the latch arms 122, 124.

The cutout 130 in the latch arm 122 and the cutout 132 in the latch arm124 are configured so as to extend over protrusions on deployed latchplates 146, 148 located at the forward end of the bottom panel 38. Thedeployed latch plates 146, 148 lie below the path of the rectangularmotor plate 62 and the ramp platform 28.

When the ramp platform 28 is fully deployed, the cutouts 130, 132 extendover the deployed latch plates 146, 148 (FIGS. 20 AND 22), preventingmovement of the rectangular motor plate 62 and the ramp platform 28. Inthis manner, the latch mechanism 120 acts as a dual locking mechanism tohold the rectangular motor plate 62 and the ramp platform 28 in thedeployed position. A spring 150 is attached to the rearward, distal endof the long pivot arm 140, and biases the latch arms 122, 124 towardcounterclockwise rotation so that cutouts 130, 132 maintain lockingengagement with the deployed latch plates 146, 148. To overcome thislocking engagement, the solenoids 144 are actuated, causing thetriangular plate 142 to retract and rotate the latch arms 122, 124 inthe clockwise direction, thereby releasing the deployed latch plates146, 148 from the cutouts 130, 132 (FIGS. 21 and 23).

The latch arms 122, 124 include rounded front ends having taperedleading sections 152, 154. The tapered leading sections 152, 154 causethe latch arms 122, 124 to engage and roll over the deployed latchplates 146, 148 as the rectangular motor plate 62 and the ramp platform28 are extended to the deployed position. The tapered leading sections152, 154 continue to rotate the latch arms 122, 124 until the cutouts130, 132 snap into place onto the deployed latch plates 146, 148 whenthe ramp platform 28 is fully deployed.

The cutout 134 on the rearward end of the latch arm 124 is configured tofit over a stowed latch plate 156 at the rearward portion of therectangular enclosure 24. The stowed latch plate 156 is located on thebottom panel 38, and is sized so as to fit under the rectangular motorplate 62 when the ramp platform 28 is stowed. The rearward edge of thesecond latch arm 124 includes a tapered trailing section 158 designed toengage and roll over the latch plate 156 during retraction of the rampplatform 28. Thus, the engagement of the cutout 134 with the stowedlatch plate 156 acts as a locking mechanism to hold the ramp platform 28and rectangular motor plate 62 in position when the ramp platform is inthe stowed position.

In use, the low floor bus 22 reaches a destination and the ramp platform28 is deployed. During travel, the ramp platform 28 is maintained in thestowed position (FIG. 9), and is held in place by the contact of thecutout 134 of the second latch arm 124 on the stowed latch plate 156. Todeploy the ramp platform 28, the driver of the low floor bus 22 pressesa deploy switch (not shown), which actuates the solenoids 144, releasingthe cutout 134 from the stowed latch plate 156. Then, the electric motor72 is powered causing the drive pulley 76 to rotate. Rotation of thedrive pulley 76 causes the drive pulley 76 to move along the drive belt80, advancing the rectangular motor plate 62 and the ramp platform 28within the rectangular enclosure 24. At the beginning of this movement,the leading end of the ramp platform 28 engages the V-shaped bracket 44on the hinged closure panel 42, causing the hinged closure panel toswing downward and expose the inside of the rectangular enclosure 24.During the beginning of extension of the ramp platform 28 and therectangular motor plate 62, the bearing blocks 116 move along andbetween the guide bars 46 and the bottom flange support bearings 54. Thebearing blocks 116 extend beyond the end of the guide bars 46 and thebottom flange support bearings 54 after a short extension of the rampplatform 28.

During extension of the ramp platform 28 and the rectangular motor plate62, the bearing strips 64 on the outer edges of the rectangular motorplate are guided below the lower surface of guide bars 46, and ridealong the upper surface of the bottom flange support bearings 54. Inaddition, the outer edges of the rectangular motor plate 62 and theouter side edges of the ramp platform 28 ride along the upper surface ofthe bottom flange support bearings 54. The circular bearings 88 aretrapped between the bottom flange support bearings 54 and the guide bars46 during this extension.

As the ramp platform 28 extends outward and more than half of the rampplatform extends out of the rectangular enclosure 24, the weight of theforward end of the ramp platform cantilevers the rearward end of theramp platform upward around the tapered leading edge 55 of the bottomflange support bearings 54, pressing the circular bearing 88 upwardagainst the lower surface of the guide bars 46. The serpentine profileof the lower edge of the guide bars 46 causes the circular bearings 88to act as cam followers that engage and are influenced by the serpentineprofile to control the ramp platform's angle with respect to therectangular enclosure 24.

As the circular bearings 88 reach the rear junctures 48 of the guidebars 46 (FIG. 10), the circular bearings begin an upward climb towardthe peak 50 of the guide bars. The torque shaft 82, however, remainsadjacent to the bottom flange support bearings 54 because the torqueshaft is attached to the bearing strips 64, which are confined frommovement upward by the lower surface of the guide bars 46. Thus, thelever arms 84 rotate about the torque shaft 82 so that the curved slots86 extend almost straight upward relative to the rectangular motor plate62 (FIG. 11).

After the circular bearings 88 have reached the peaks 50 (FIG. 12), thecircular bearings begin a downward motion (FIG. 13) toward the forwardjunctures 52 (FIG. 14). When the circular bearings 88 reach the peaks50, the angle of the ramp platform 28 with the bottom panel 38 is thesame as the angle of the section of the guide bars 46 between the peak50 and forward juncture 52 with the bottom panel. Thus, as the circularbearings 88 move downward toward the forward junctures 52, the rampplatform 28 extends in a linear manner along an angle which is equal tothe lower surface of the guide bars 46.

As the ramp platform 28 approaches the last few inches of thedeployment, the circular bearings 88 extend beyond the ends of the guidebars 46 and the bottom flange support bearings 54 (FIG. 15). By thistime, the beveled leading edge 114 of the ramp platform 28 is resting onthe ground. After a little more advancement of the ramp platform 28, thecurved slots 86 on each of the lever arms 84 engage the pins 56 (FIG.16). The pins 56 act as abutment surfaces for engaging and rotating thelever arms 84. The engagement of the curved slots 86 with the pins 56stops advancement of the top portions of the lever arms 84, causing thelever arms to rotate about the torque shaft 82. As is shown sequentiallyin FIGS. 17, 18, and 8, the lever arms 84 continue to rotate, liftingthe trailing end of the ramp platform 28 upward until the trailing endof the ramp platform is aligned with the upper cross-member 58.

During the final advancement of the ramp platform 28, the lever arms 84contact the V-shaped brackets 44 on the hinged closure panel 42, causingthe hinged closure panel to pivot downward clear of the underside of thedeployed ramp platform 28. In addition, the leading edges of the bearingstrips 64 are captured between the forward juncture 52 of the guide bars46 and the bottom flange support bearings 54. This capturing addsstability to the fully-deployed ramp platform 28. When the ramp platformis fully deployed, the latch arms 122, 124 lock onto the deployed latchplates 146, 148.

The curved slots 86 are toleranced to influence control of the pivot ofthe lever arms 84 during travel. Specifically, the curved slots 86 andthe lever arms 84 are arranged so that the trailing end of the rampplatform 28 moves substantially straight upward and downward after thebearings 88 have extended beyond the end of the guide bars. During thismovement, concave rear surfaces 152 of the curved slots 86 move alongthe pins 56. This movement helps in retracting the ramp platform 28,because it forces the lever arms 84 to pivot downward and not rely ongravity. The torque shaft 82 provides continuity from one lever arm 84to the other should non-uniform loads be applied to the ramp platform28.

As can be best seen in FIG. 6, the serpentine profile of the guide rail46 and the substantially straight configuration of the bottom flangesupport bearings 54 creates a gap 154 between the guide rail and thebottom flange support bearings underneath the peak 50. The gap 154permits free movement of the circular bearings 88 between the guide rail46 and the bottom flange support bearings 54 so that the ramp platform28 can extend at a variety of different angles relative to therectangular enclosure 24. This freedom of movement of the circularbearings 88 permits the ramp platform 28 to extend in a variety ofdifferent angles relative to the rectangular enclosure 24, allowing theramp platform 28 to be deployed onto surfaces having varying heights. Ifthe leading end of the ramp platform 28 comes into contact with theground, the weight of the ramp platform no longer cantilevers thecircular bearings 88 into contact with the guide rail 46. Instead, thecircular bearings 88 lower toward the bottom flange support bearings 54and the ramp platform 28 continues to extend, with the leading edge ofthe ramp platform dragging on the ground, until the ramp platform isfully extended. In this manner, the ramp platform 28 can be deployedonto different surfaces having varying heights.

As is best shown in FIG. 5, a limit switch 160 is located on therectangular motor plate between the solenoids 144 and the electricalmotor 72. The limit switch 160 includes an arm 162 that engages a firststop 164 (near the upper cross member 58, FIG. 3) upon full deploymentof the ramp platform 28, and a second stop 166 (adjacent the end panel36, FIG. 4) upon full retraction of the ramp platform 28. The limitswitch 160 signals the control logic system for the ramp assembly 20that the ramp platform is in the fully stowed or fully deployedpositions. Once the ramp platform 28 is in either position, power isdisconnected from the electrical motor 72.

To retract the ramp platform 28, the driver actuates a “stow” button(not shown), which causes the solenoids 144 to actuate and release thelatch arms 122, 124 from the deployed latch plates 146, 148. Then, theelectric motor 72 is powered causing the drive pulley 76 to rotate.Rotation of the drive pulley 76 causes the drive pulley to move alongthe drive belt 80, causing the rectangular motor plate 62 to movebackward, rotating the lever arms 84, and thereby lowering the rearwardend of the ramp platform 28. As described above, the front edge of theguide bars 46 include a sloped front edge 53 so as to direct thecircular bearings 88 to between the guide bar and the bottom flangesupport bearing 54. The tapered leading edge 55 of the bottom flangesupport bearings 54 also helps to guide the circular bearings 88 intothe cam slots formed by the guide bars 46 and the bottom flange supportbearings 54.

Once the pins 56 are released from the curved slots 86 of the lever arms84, the lever arms 84 cease rotation, and the ramp platform 28 beginsretraction. As the ramp platform 28 is retracted, the circular bearings88 once again engage the lower surfaces of the guide bars 46, and movealong the serpentine path of the guide bars until at least half of theramp platform 28 is within the rectangular enclosure 24, and the weightof the ramp platform is upon the bottom flange support bearings 54.During this movement, the rectangular motor plate 62 continues toretract and pull the ramp platform 28 toward the rear portion of therectangular enclosure 24. The latch arm 124 eventually engages and rollsover the stowed latch plate 156, and locks in place. The limit switch160 is engaged by the stop 166, and power is cut to the electrical motor72. At the end of the retraction of the ramp platform 28, the hingedclosure panel 42 closes. The stowed ramp platform 28 is now ready fortravel.

On occasions when electrical power to the ramp assembly 20 should fail,a manual unlatching mechanism 180 enables the operator to release theramp platform 28 from the deployed or stowed positions. The operator maythen push the ramp platform 28 rearward to stow it in the rectangularenclosure 24. Alternatively, if electrical power is unavailable, amechanic can operate the manual unlatching mechanism 180 to release theramp platform 28 in order to physically extend the ramp platform forservicing.

The manual unlatching mechanism 180 (FIG. 19) includes a cam lever 182located adjacent to and between the deployed latch plates 146, 148. Thecam lever 182 is pivotally attached at one end to a pin 183 that isfixed to the bottom panel 38. The opposite end of the cam lever 182includes a convex surface 181.

A wire cable 184 is attached to the rear end of the cam lever 182. Theforward end of the cam lever 182 is attached to an extension spring 186(FIG. 24). The wire cable 184 is attached at an opposite end to aT-handle 194 (FIG. 2) having a threaded rod 196. The threaded rod 196(FIG. 19) is inserted through and supported by a guide tube 198 attachedto the rectangular enclosure 24. The guide tube 198 also limits the fullstroke of the T-handle 194 by its length. The wire cable 184 extendsrearwardly from the cam lever 182 along the top surface of the bottompanel 38 and wraps around a wire rope pulley 200 located at the endpanel 36 adjacent the structural channel 60. From the wire rope pulley200, the wire cable 184 extends along the rearward interior of therectangular enclosure 24 to a second wire rope pulley 202 that extendspartly through an opening in the rearward portion of the side panel 34.At the second wire rope pulley 202, the wire cable 184 exits therectangular enclosure 24 and extends toward the forward end of therectangular enclosure terminating at the threaded rod 196.

The wire cable 184 includes a wire rope ball shank 204 swaged to thewire cable along the rearward interior of the rectangular enclosure,between the two wire cable pulleys 200, 202, adjacent to the locationwhere the latch arm 122 extends when the ramp platform 28 is in thestowed position. The latch arm 122 includes a V-notch 208 at itsrearward end which is designed to capture the wire cable 184 when theramp platform 28 is retracted to the stowed position.

When the ramp platform is in the stowed position, the wire cable 184extends through the V-notch 208 in the rear portion of the latch arm 122(FIG. 25). If power is cut to the ramp assembly 20, the T-handle 194 canbe pulled to operate the manual unlatching mechanism 180. When theT-handle 194 is pulled, the wire cable extends along the V-notch 208until the wire rope ball shank 204 engages the rearward end of the latcharm 122, and causes the latch arm 122 (FIG. 26), as well as the secondlatch arm 124 (FIG. 28) to rotate. Rotation of the second latch arm 124causes the cutout 134 to release from the stowed latch plate 156, andthe ramp platform 28 is released. The ramp platform can then be manuallywithdrawn.

When the ramp platform 28 is fully deployed and power is cut to the rampassembly 20, the manual unlatching mechanism 180 can be operated so asto release the ramp platform 28 so that it can be manually retracted.The rear end of the latch arm 122 includes a protrusion 210 (FIG. 20).This protrusion 210 is engaged by the camming surface 181 of the camlever 182 when the ramp platform 28 is fully deployed and the T-handle194 is pulled. Engagement of the protrusion 210 by the cam lever 182causes the latch arm 122, as well as the latch arm 124, to rotate andrelease the deployed latch plates 146, 148 (FIGS. 21 and 23). In thismanner, the manual unlatching mechanism 180 unlocks the ramp platform 28and permits manual retraction of the ramp platform.

A disconnect coupling or clutch (not shown) can be coupled between theelectrical motor 72 and drive shaft 74 to allow selective release of thedrive pulley from the electrical motor 72, which would ease manualextension or retraction of the ramp mechanism. In addition,anti-friction bearings (not shown) at the shafts for the drive pulley 76and idler pulleys 78 could reduce the force required to manually extendor retract the ramp platform 28. Finally, the drive belt 80 could beloosened or removed to reduce resistance to manual retraction orextension of the ramp platform 28.

The ramp assembly 20 of the present invention provides severaladvantages over prior art ramps. The lever arms 84 and pins 56 provide amechanism by which the ramp platform 28 can be extended and the trailingend of the platform can be lifted, all in one translational movement.Thus, additional motors or mechanisms are not needed to lift the reartrailing end of the ramp platform 28. In addition, a transitional plateor other mechanism is not needed to provide a smooth transition betweenthe ramp platform and the floor of the low-floor bus 22.

The present invention also provides the convenient reciprocatingmechanism 26 that includes an electric motor 72 that is mounted forreciprocating motion with the ramp platform 28. This design saves space,and does not require a mounting structure for a motor underneath orbehind the rectangular enclosure 24. The coiled electrical cable 90permits accessible electrical power for the electric motor 72 and othercomponents on the rectangular motor plate 62. Although the powersupplied is disclosed as an electric motor 72, it is to be understoodthat hydraulic and other power sources could be used.

The ramp assembly 20 of the present invention also provides the manualunlatching mechanism 180, which permits manual release of the rampplatform 28 at the fully extended or retracted positions. The rampplatform 28 can then be manually extended or retracted.

FIGS. 29-51 show an alternate embodiment of a ramp assembly 300embodying the present invention. As with the first described rampassembly 20, the ramp assembly 300 includes a rectangular enclosure 24,a reciprocating mechanism 26, and a ramp platform 28. Like parts on theramp assembly 20 and the ramp assembly 300 include like referencenumerals.

The ramp assembly 300 includes springs 301 (best shown in FIGS. 30 and32) that are attached to the lever arms 302. One of the springs 301 isattached at one end to an eyelet 303 at the upper extension of one ofthe lever arms 302. The opposite end of the spring 301 is attached to aneyelet 304 located at the rear inner edge of the adjacent bearing strip64. A similar spring 301 is mounted on the opposite side of therectangular motor plate 62 for attachment to the other lever arm 302.

The springs 301 are helpful in manual deployment of the ramp platform28. It has been found that when the ramp platform 28 is manuallydeployed, the trailing end of the ramp platform very often does not liftupward high enough and therefore advance the rectangular motor plate 62to engage the latch arms 122, 124 on the deployed latch plates 146, 148.The springs 301 overcome this problem by providing a lifting force thatraises the trailing end of the ramp platform 28, and therefore aids inadvancement of the rectangular motor plate 62, during manual extension.

Because the springs 301 cause the leading ends of the lever arms 302 tobe biased upwards, the top edges 305 (FIGS. 32 and 33) of the lever arms302 are shaped differently than the top edges of lever arms 84 for thefirst ramp assembly 20. Preferably, the top edges 305 slope slightlyupward so that the top edges 305 can smoothly ride along and not beimpeded by the pins 56. The slope of the top edges 305 causes the leverarms 302 to move along the pins 56, and permits a smooth, extension ofthe trailing end of the ramp platform 28, while guiding the curved slots86 to the pins 56.

The springs 301 preferably have a sufficient spring constant and aresized so that they support approximately one-half the weight of the rampof platform 28. The springs 301 therefore counterbalance the trailingedge of the ramp platform 28 upward, thus allowing a smooth transitionfor the curved slots 86 to engage the pins 56 which also allowsadvancement of the rectangular motor plate 62 a sufficient distance sothat the deployed latch arms 122, 124 engage, roll over, and latchagainst the deployed latch plates 146, 148. By providing this function,the springs 301 enable an operator to manually extend the ramp platform28 until the ramp platform is fully deployed without expending muchextra effort as the trailing end of the ramp platform is raised.

The lever arm 302 includes a removable cam follower 306 (best shown inFIG. 33) attached at its leading end. The removable cam follower 306serves the function of the circular bearing 88 of the previousembodiment, and additionally provides a convenient manner of removingthe ramp platform 28.

The leading end of the lever arm 302 includes a half circular open end307, the opening of which faces forward, and two threaded holes 308spaced rearward therefrom. The removable cam follower 306 is teardropshaped and includes a sleeve 309 extending off its rear surface at thelarger portion of the tear drop shape. Two holes 310 are provided thatmatch with the threaded holes 308 on the lever arm 302 and that arecountersunk to receive the heads of cap bolts 311 (FIG. 41). A largerhole 312 that is concentric with the sleeve 309 is provided at thelarger portion of the teardrop-shape of the removable cam follower 306.The larger hole 312 is aligned so that when the bolts 311 are extendedthrough the small holes 310 and threaded into the threaded holes 308 onthe lever arm 302, the larger hole 312 is concentric with the halfcircular open end 307 of the lever arm 302.

The larger hole 312 and sleeve 309 on the cam follower 306 are designedso that they fit over a pin 314 that extends sideways outward from thetrailing end of the ramp platform 28. A similar pin 314 is located onthe opposite side of the ramp platform 28 and is received within asimilar removable cam follower 306 attached to the other lever arm 302.The lever arms 302 and removable cam followers 306 are spaced apart sothat the pins 314 on opposite sides of the ramp platform 28 are receivedby and held against the cam followers 306 when the cam followers aretightened against the lever arms 302 by the cap bolts 311. The sleeve309 is also seated against the half circular open end 307 of the leverarm 302.

The cap bolts 311 include a tool receiving pattern such as a hex sockethead. By placing a tool into the tool receiving pattern and rotating thebolts 311, one of the removable cam followers 306 can be loosened andremoved, releasing the respective pin 314 on that side of the rampplatform 28. The ramp platform 28 can then be lowered to move away fromthe lever arm 302, and then can be pulled so that the opposite pin 314is pulled out of the hole 312 and sleeve 309 on the opposite removablecam follower 306. In this manner, the ramp platform 28 is removed fromthe ramp assembly 300 by disassembly of only one removable cam follower306. This feature provides a simpler disconnect procedure for the rampplatform 28 if repair or maintenance needs to be performed.

The removable cam followers 306 are preferably formed from alow-friction bearing material. This material permits the removable camfollowers 306 to freely slide between the support bearings 54 and guidebars 46.

It has been found that upon manual release by the manual unlatchingmechanism 180 of the deployed latch arms 122, 128 from the deployedlatch plates 146, 148, the weight of the ramp platform 28 pulls thelever arms 302 down a sufficient amount to retract the rectangular motorplate 62 into the rectangular enclosure 24 so that when the manualunlatching mechanism 180 is released, the deployed latch arms do notre-engage the deployed latch plates. To provide a similar function, apush-off spring mechanism 320 (best shown in FIG. 31) is provided on therectangular motor plate 62 to initiate movement of the rectangular motorplate and the ramp platform 28 upon manual release in the stowedposition. The push-off spring mechanism 320 initiates movement of therectangular motor plate 62 upon manual release of the cutout 134 on therearward end of the latch arm 124 from the stowed latch plate 156.

As can be seen in FIG. 31, the push-off spring mechanism 320 includes abracket 322 extending perpendicularly upward from the face of therectangular motor plate 62. The bracket 322 includes a hole (not shown)extending parallel to the rectangular motor plate 62. A bolt 324 extendsthrough a spring 326, into a spring retaining sleeve 328, and outthrough the hole. A nut 330 is threaded onto the end of the bolt thatextends out of the hole. The opposite end of the bolt 324 is positionedso that it extends slightly rearward beyond the end of the rectangularmotor plate 62. In operation, the head of the bolt 324 engages the endpanel 36 of the rectangular enclosure 24. When the ramp platform 28 isin the stowed position, the spring 326 is slightly compressed. Actuationof the manual unlatching mechanism 180 causes the spring 326 to relax(extend) and push the rectangular motor plate 62 away from the end panel36. This movement by the rectangular motor plate 62 away from the endpanel 36 is sufficient to prevent the cutout 134 on the rearward end ofthe latch arm 124 from re-engaging the stowed latch plate 156 aftermanual release.

The ramp assembly 300 also incorporates a delay circuit 334 (FIG. 34)for more efficient operation of the solenoids 144 and the motor 72.Applicants have found that when power is supplied to the rectangularmotor plate 62, the motor 72 begins movement of the rectangular motorplate 62 faster than the solenoids 144 release the latch mechanism 120.This lag in movement by the latch mechanism 120 is due largely to theweight of the latch mechanism 120. The motor 72 has a tendency toattempt to move the rectangular motor plate 62 immediately uponreceiving power and before the latch arms 122, 124 have released fromeither the deployed latch plates 146, 148, or the stowed latch plate156. To solve this problem, the present invention provides the delaycircuit 334 shown in FIG. 34.

The delay circuit 334 introduces a time delay between actuation of thesolenoids 144 and start of the motor 72. The delay circuit 334 utilizesdelay circuitry (not shown, but well known in the art) to properly spacethe time between the start of the solenoids 144 and start of the motor72, so that the latch arms 122, 124 are fully released before the motor72 attempts to move the rectangular motor plate 62.

Applicants have also found it to be advantageous to use similar timingcircuitry within the delay circuit 334 to deactuate the solenoids 144simultaneously with start of the motor 72. Because start of the motor 72occurs more rapidly than deactuation of the solenoids 144 can causereturn of the latch mechanism 120 by the spring 150 and the returnstroke of the solenoids 144, the motor moves the rectangular motor plate62 before the latch arms 122, 124 can re-engage the latch plates. Inaddition, by deactuating the solenoids 144 at the same time the motor 72is started, the solenoids and the motor are not powered at the sametime. This results in less power having to be provided to therectangular motor plate 62.

A sensor switch 340 (FIG. 31) is provided on the trailing end of therectangular motor plate 62. The sensor switch 340 engages the end panel36 when the rectangular motor plate 62 is in the stowed position. Thesensor switch 340 provides an interlock signal to the low floor bus 22upon engagement of the sensor switch 340 with the end panel 36. Theinterlock signal is an indication that the ramp platform 28 is in thestowed position. The interlock signal can be wired to an interlock inthe bus electrical system so as to prevent travel of the bus when theramp platform 28 is not in the stowed position. Alternatively, theinterlock signal can light an indicator lamp at the control panel forthe bus driver, or other indicators could be provided.

The ramp assembly 300 includes an adjustable deployed latch plate 342(shown in relation to the ramp assembly in FIG. 51). The underside ofthe adjustable deployed latch plate 342 is shown in FIG. 36. Theadjustable deployed latch plate 342 includes a rectangular raisedsection 344 that extends along the bottom side of the deployed latchplate. The rectangular raised section 344 is configured to fit within arectangular elongate cutout 346 in the bottom panel 38 (FIG. 35). Therectangular elongate cutout 346 is longer than the rectangular raisedsection 344, but only slightly larger in width, which permits theadjustable deployed latch plate 342 to fit within and slide along therectangular elongate cutout. The adjustable deployed latch plate 342includes a number of threaded holes 348 (FIG. 36) extending into thebottom of the latch plate and located on opposite sides of therectangular raised section 344. The threaded holes 348 align withelongate slots 350 on the bottom panel 38 (FIG. 35). Screws 352 extendthrough the elongate slots 350 into the threaded holes 348.

A rod 354 is threaded into a female threaded hole 356 that extends intothe aft section of the adjustable deployed latch plate 342. The threadedrod 354 includes a tool receiving pattern 358, such as the head of abolt, at its distal end. A five-sided box 359 is attached to the aft endof the adjustable deployed latch plate 342, over the end of the threadedrod 354. The five-sided box 359 keeps dirt and other road grime fromentering the ramp assembly 300 through the rectangular elongate cutout346.

An abutment surface in the form of a metal protrusion 360 is located onthe top surface of the bottom panel 38 just rearward of the end of therectangular elongate cutout 346. The metal protrusion 360 can be formedintegral with the bottom panel 38, punched out of the bottom panel,welded integral with the bottom panel, or can be formed in otherconventional methods.

In practice, the adjustable deployed latch plate 342 is arranged so thatthe rectangular raised section 344 extends into the rectangular elongatecutout 346. The screws 352 extend through the elongate slots 350 andinto the threaded holes 348. The screws 352 are not tightened until theadjustable deployed latch plate 342 is properly aligned relative to thelatch arm 124. To properly align the adjustable deployed latch plate342, the rectangular raised section 344 is slid along the rectangularelongate cutout 346 until the adjustable deployed latch plate 342 isapproximately aligned with the cutout 132 on the latch arm 124 when therectangular motor plate 62 and the ramp platform 28 are in the fullydeployed position. A tool (not shown) that fits on the tool receivingpattern 358 rotates the threaded rod 354 until the threaded rod abutsagainst the metal protrusion 360. Further rotation of the threaded rod354 moves the adjustable deployed latch plate 342 toward the front ofthe rectangular elongate cutout 346. By maintaining the threaded rod 354snugly against the metal protrusion 360, rotation of the threaded rodprovides minute adjustments of the adjustable deployed latch plate 342.In this manner, the adjustable deployed latch plate 342 can be alignedso that latch arm 124 fits precisely over the latch plate when the rampplatform is in the fully deployed position.

Preferably, a second adjustable deployed latch plate 362 (FIG. 51) isprovided for alignment with the cutout 130 of the other latch arm 122.The details of the second adjustable deployed latch plate are not shown,but could be similar to the adjustable deployed latch plate 342described. The adjustable deployed latch plates 342, 362 provide amethod for properly aligning the latch plates with the latch arms 122,124 that is accessible from the bottom (outside) of the rectangularenclosure 24.

A manual unlatching mechanism 366 is provided for the ramp assembly 300that is substantially the same as the manual unlatching mechanism 180described with reference to the ramp assembly 20. However, a differenthandle 368 (best shown in FIG. 41) is utilized in the manual unlatchingmechanism 366. The handle 368 includes a loop 370 at a forward end thatis attached to a hexagonal rod 372. The hexagonal rod 372 extendsthrough a hexagonal slot 374 in a bracket 376 that extends perpendicularfrom the side panel 34 of the rectangular enclosure 24. The hexagonalrod 372 includes a rounded circumferential groove 378 spaced from thedistal end of the hexagonal rod. Just forward of the rounded groove 378,a cap bolt 380 extends radially into the hexagonal rod 372. The head ofthe cap bolt 380 extends out of the side of the hexagonal rod 372.

The front end of the handle 368 extends through a hole (not shown) inthe bracket 41. The loop 370 is normally positioned between the bracket41 and the hinged closure panel 42.

A release tool 382 (FIG. 50) is used to unlatch the manual unlatchingmechanism 366. The release tool includes a handle 384, a hook 386, and around tube (or rod) 388 extending from the handle to the hook. The hook386 is sized so that it can fit within the loop 370 of the handle 368,and can extend over one side of the loop.

In practice, the release tool 382 is gripped at the handle 384 by anoperator, and the hook 386 is extended into the loop 370 of the handle368 of the manual unlatching mechanism 366. The operator. may have toopen the hinged closure panel 42 to access the handle 368. The operatorpulls outward on the release tool 382, which pulls outward the handle368. The handle 368 is attached to the wire cable 184, and pullingoutward on the handle rotates the latch arms 122, 124 as was describedwith reference to the first ramp assembly 20.

The hexagonal shapes of the hexagonal rod 372 and the hexagonal slot 374prevent rotation of the hexagonal rod and maintains the loop 370 inalignment so that it can extend out of and retract into the frame 41.The hexagonal rod 372 is pulled outward until the cap bolt 380 abutsagainst the bracket 376. The contact of the cap bolt 380 with thebracket 376 precludes further extension of the hexagonal rod 372.

During extension of the handle 368, the manual unlatching mechanism 366releases the latch arms 122, 124 from the deployed latch plates 342, 362or the stowed latch plate 156. After the latch arms 122, 124 arereleased, the operator can stop pulling on the handle 368, and thespring 186 returns the handle 368 into position against the bracket 41.Although actuation of the manual unlatching mechanism 366 is describedwith reference to use of a release tool 382 by an operator, it is to beunderstood that the handle 368 of the manual unlatching mechanism 366could be gripped by the fingers of an operator, or could be pulledoutward using other methods.

The ramp assembly 300 incorporates a drive belt clutch mechanism 398(FIG. 44) and a manual belt release mechanism 400 (FIG. 38). In summary,the two mechanisms 398, 400 work together so that a belt releaseassembly 402 of the manual belt release mechanism 400 relaxes the drivebelt 404 (i.e., removes tension), and the drive belt clutch mechanism398 separates the drive belt 404 from operation of the motor 72. In thismanner, the ramp platform 28 can be manually extended and retractedwithout the resistance of the motor 72 against the drive belt 404. Themanual belt release mechanism 400 will be described below, followed by adescription of the drive belt clutch mechanism 398.

The manual belt release mechanism 400 includes a belt release assembly402 (FIG. 39) that is attached to the drive belt 404. The belt releaseassembly 402 includes a toothed belt clamp 406. The toothed belt clamp406 is a flat plate with a series of slots 408 extending from front toback along its center and a cutout 410 just forward of the slots.Threaded holes 412 are aligned along both sides of the slots 408. At thefront, top end of the toothed belt clamp 406 are two triangular cutoutrecesses 414.

A separate belt tensioner link 416 (FIG. 39) is pivotally mounted fromthe apex of each of the triangular cutout recesses 414. Pins 418 extendthrough each of the belt tensioner links 416, through the toothed beltclamp 406 at the apex of the triangular cutout recesses 414, and into anadditional set of belt tensioner links 420 on the opposite side of thetoothed belt clamp 406. Thus, each pin 418 acts as a pivotal mount forboth a belt tensioner link 416 located on the top of the toothed beltclamp 406 and located within the triangular cutout recesses 414, and abelt tensioner link 420 located underneath the toothed belt clamp 406.The belt tensioner links 416, 420 extend forward to opposite sides ofeccentric pivot mounts 422, 424 (best shown in FIG. 43). The eccentricpivot mounts 422, 424 each have a flanged bearing 428 extendingtherethrough. L-brackets 430, 431 extend upward from the eccentric pivotmounts 422, 424.

The eccentric pivot mounts 422, 424 are rotatably mounted on pins 456that extend into the structured channel 60. The tops of the pins 456 areshown in FIG. 30, and the bottoms of the pins are shown in FIG. 42. Thebelt tension links 416, 420 are pivotally mounted about pins 426 (oneshown in FIG. 43, one shown in FIG. 38) that are eccentrically mountedabout the pin 456 on the eccentric pivot mounts 422, 424.

A drive cam 432 (FIG. 39) is attached to the L-bracket 430 of theeccentric pivot mount 422, and a driven cam 434 is attached to theL-bracket 431 of the opposite eccentric pivot mount 424. The drive cam432 includes a half circular plate 435 having teeth 436 along an outeredge of the circumference of the half circle, and a lever arm 438 fixedat one end of the circumference of the half circle. The lever arm 438extends outward in a plane from the plate 435 and bends at a distal endat a right angle to form a spring attachment 440. A pin 442 is locatedadjacent to the angle formed between the spring attachment 440 and thelever arm 438.

The driven cam 434 includes a quarter circle plate 443 having teeth 444along an outer edge of the circumference of the quarter circle, andarranged to engage the teeth 436 on the drive cam 432. The drive cam 432and the driven cam 434 both include flanged bearings 446 aligned withthe flanged bearings 428 in the eccentric pivot mounts 422, 424. Thepins 456 extend into the pairs of flanged bearings 446, 428.

Turning now to FIG. 37, the belt release assembly 402 is mounted justbelow the structural channel 60 at the rearward portion of therectangular enclosure 24 (location relative to the entire ramp assembly300 is shown in FIG. 51). A pair of grooved bearings 450 are mounted onopposite sides of the structural channel 60 to slidingly receive theside edges of the toothed belt clamp 406. Teeth on the drive belt 404extend between the slots 408 on the toothed belt clamp 406. A drive beltclamp plate 452 is attached over the drive belt 404 and the toothed beltclamp 406 so as to capture the drive belt 404. The drive belt clampplate 452 is held in position against the toothed belt clamp by a seriesof fasteners 454 that extend through holes (not shown) in the drive beltclamp plate 452 and into the threaded holes 412 in the toothed beltclamp 406.

Referring now to FIG. 38, the pins 456 extend through the top of thestructural channel 60 and downward through the flanged bearings 446,428, on the eccentric pivot mounts 422, 424 and the drive cam 432 anddriven cam 434. The drive cam 432 and driven cam 434 are thus mountedfor rotation with the eccentric pivot mounts 422, 424 about the pins456.

A pair of springs 460 (full mounting shown in FIG. 37) are each attachedat one end to a bracket 462 on the back side of the end panel 36, andattached at the other end to the spring attachment 440 on the lever arm438 of the drive cam 432. A belt release cable 464 is attached at thepin 442 on the lever arm 438 of the drive cam 432. The belt releasecable 464 extends from the pin 442 along the back of the end panel 36(FIG. 51) through a pulley 466 and forward to a handle 470 mounted justbelow the handle 368 for the manual unlatching mechanism 366. The handle470 includes a similar structure to the handle 368, including a loop370, hexagonal rod 372, rounded groove 378, and cap bolt 380. The handle470 for the manual belt release mechanism 400 extends through ahexagonal slot 472 in the bracket 376 that includes a cutout 474. Thecutout 474 is arranged opposite the side panel 34 and extends radiallyoutward from the circumference of the hexagonal slot 472. The cutout 474is slightly larger than the head of the cap bolt 380, the function ofwhich will be described in detail below. The handle 470, like the handle368, is accessible between the bracket 41 and the hinged closure panel42 (FIG. 41).

The operation of the manual belt release mechanism 400 will now bedescribed. If manual retraction or deployment of the ramp platform 28 isdesired, the manual belt release mechanism 400 is actuated so as torelease the drive belt 404. To do this, the hinged closure panel 42 ismanually opened and the loop 370 of the handle 470 is grasped by thehook 386 of the release tool 382. The operator pulls on the release tool382, causing the handle 470 to extend outward from the bracket 41 (FIG.40). Pulling the handle 470 outward in this manner causes the head ofthe cap bolt 380 to be pulled through the cutout 474. The rounded groove378 is aligned with the hexagonal slot 472, which permits the handle 470to be rotated 90 degrees to extend downward (FIG. 41) so that the headof the cap bolt 380 is no longer aligned with the cutout 474. In thisposition, the handle 470 cannot retract, because the contact between thehead of the cap bolt 380 and the bracket 376 prevents movement of thehandle rearward. The handle 470 is positioned so that it holds thehinged closure panel 42 open, allowing the operator access to the handle368 for the manual unlatching mechanism 366.

Pulling outward on the handle 470 causes the belt release assembly 402to release tension on the drive belt 404. In normal, tensioned mode ofthe drive belt 404, the belt release assembly 402 is in the positionshown in FIG. 39. In this arrangement, the belt tension links 420, 416are in an over-center eccentric position. That is, the tension in thedrive belt 404 and the eccentric mounting of the belt tension links 416,420 on the eccentric pivot mounts 422, 424 biases the drive cam 432 andthe driven cam 434 into the positions shown in FIG. 39, and in adirection opposite of the arrows shown on the surfaces of the drive camand driven cam. The springs 460 also pull the lever arm 438 andtherefore the drive cam 432 in a direction that is opposite the arrows.

By pulling on the handle 470, the belt release cable 464 pulls the leverarm 438 so that the drive cam 432 and driven cam 434 are rotated in thedirection of the arrows in FIG. 39. At the beginning of this rotation,the belt tension links 416, 420 resist movement because of theover-center location of the belt tension links relative to theireccentric mounting on the eccentric pivot mounts 422, 424. Once thisinitial resistance is overcome, the pins 426 at the upper end of thebelt tension links 416, 420 are rotated by and about the eccentric pivotmounts 422, 424 to the opposite side of the axis of rotation of thedrive cam 432 and the driven cam 434 (i.e., the pins 456). The pullingforce on the belt release cable 464 then causes further rotation of thedrive cam 432 and the driven cam 434 to the position shown in FIG. 43.In this position, the belt tension links 416, 420 have been rotated bythe eccentric pivot mounts 422, 424 so that the pins 426 are forward ofthe pins 456. Moving the belt tension links 416, 420 eccentrically inthis manner moves the toothed belt clamp 406 forward in the groovedbearings 450. This movement forward releases the tension on the drivebelt 404, and creates slack in the drive belt.

To re-tension the drive belt 404, the handle 470 is rotated so as toalign the cap bolt 380 with the cutout 474, and the handle 470 isallowed to retract under the tension of the springs 460. Preferably, thetension of the springs 460 is sufficient to withdraw the handle 470 andovercome the tension of the drive belt 404 so as to pull the belttension links 416, 420 back to the over-center position (shown in FIG.39). Upon full release of the handle 470 and return of the belt releaseassembly to the position shown in FIGS. 37-39, the drive belt 404 isfully tensioned and locked into place. Retraction of the handle 470permits the hinged closure panel 42 to once again be closed.

The drive belt clutch mechanism is shown in FIGS. 44-47. The drive beltclutch mechanism 398 includes a drive pulley 480 mounted parallel to andbetween two idler pulleys 482 (FIG. 44). The drive pulley 480 includes aclutch groove 484 extending around its circumference and located at itscenter. The drive pulley 480 is mounted for rotation about a drive shaft486 that extends through front and rear pulley mounting plates 488, 490.The drive pulley 480 includes teeth 485 around its perimeter except atthe clutch groove 484. The teeth 485 are spaced so as to receive theteeth on the drive belt 404.

The idler pulleys 482 are mounted on idler shafts (not shown) forrotation thereon. Bolts 492 extend through spring guides 494 and throughthe pulley mounting plate 488 or 490 and into the idler shafts. Thespring guides 494 are rings with a circumferential groove.

A clutch saddle 496 (FIG. 45) rests across the top of the pulleymounting plates 488, 490, and is held in position by two springs 498.The clutch saddle 496 includes two mounting plate bars 500 attached bytwo cross braces 502. The cross braces 502 and the mounting plate bars500 form a rectangle, and the mounting plate bars extend beyond therectangle. At distal ends of the mounting plate bars 500 are spring armattachments 504 that extend downward at approximately a 90° angle to themounting plate bars. Holes 506 are located on the spring arm attachments504 for receiving the ends of the springs 498.

A clutch band 508 extends across and forms a downward loop between thetwo cross braces 502. The clutch band 508 includes two cross braceattachments 510 and a bottom rounded section 512 for fitting about theclutch groove 484 of the drive pulley 480. As can best be seen in FIGS.46 and 47, the clutch band 508 is configured such that the radius ofcurvature of the rounded section substantially matches the radius ofcurvature of the outer circumference of the teeth 485 on the drivepulley 480. Two flattened sections 514 are formed at the outer ends ofthe bottom rounded section 512 for directing the drive belt 404 awayfrom the teeth of the drive pulley 480. The clutch band 508 extendssubstantially straight upward from the flattened sections 514 to thecross brace attachments 510.

The clutch saddle 496 is preferably formed as a weldment of stiff metal,such as steel. The springs 498 are attached to the spring armattachments 504 and extend under the spring guides 494. The springs 498bias the clutch saddle downward against the upper surface of pulleymounting plates 488, 490, toward the position shown in FIG. 47.

In operation, when the drive belt 404 is tensioned, the tension of thedrive belt pulls the clutch saddle 496 upward into the position shown inFIG. 46 so that the teeth of the drive belt engage the teeth 485 of thedrive pulley 480. The drive belt 404 is wider than the clutch groove484, so it extends across the clutch groove to engage the teeth 485 onboth sides of the clutch groove. When the drive belt 404 is released bythe belt release assembly 402, the springs 498 urge the clutch saddle496 downward, and push the teeth of the drive belt 404 out of engagementwith the teeth of the drive pulley 480. In this manner, the rampplatform 28 can be extended and retracted with the drive belt 404released from the drive pulley 480 so that an operator does not have toturn the motor upon extension and retraction.

It is important that the tension of the springs 498 not be too strong soas to stretch the drive belt 404 or bend the clutch saddle 496 duringoperation. Instead, a spring tension should be selected such that theforce downward on the clutch saddle 496 by the springs 498 is sufficientto take the slack in the released drive belt 404 and move that slackdownward by the pressure of the clutch saddle 496.

The ramp platform 28 includes an elongate slot 520 along its leadingend. During manual extension of the ramp platform 28, the hook 386 onthe release tool 382 can be inserted into the elongate slot, and theoperator can pull the ramp platform 28 outward. This operation permitsthe operator to extend the ramp platform 28 without inserting hands intothe rectangular enclosure 24 or having to bend over to reach the rampplatform 28.

The components of a belt tensioner 530 for the drive belt 404 are shownin FIGS. 48 and 49. A stationary plate 532 (FIG. 49) including a groove534 for receiving the drive belt 404 is mounted to the underside of thestructural channel 60. The stationary plate 532 includes mounting holes535 on opposite sides of the groove 534. An adjustable clamp 536 (FIG.48) is mounted between the stationary plate 532 and a metal plate 537that extends under the structural channel 60. The adjustable clampincludes a series of ribs 538 extending along its middle and twoelongate slots 540 extending along the sides of the ribs. A graspingslot 542 is located at the front end of the ribs 538, and a flange 543is aligned across the front of adjustable clamp 536.

To mount the drive belt 404, the teeth of the drive belt are matchedwith the ribs 538 of the adjustable clamp 536, and the opposite, smoothside of the drive belt is arranged within the groove 534 of thestationary plate 532. Fasteners such as screws or bolts 544 (only oneshown in FIG. 52) are extended (through the holes 535 on the stationaryplate 532) through the slots 540, and into the metal plate 537. Thebolts 544 are anchored into the metal plate 537.

The bolts 544 are not tightened against the adjustable clamp 536 andstationary plate 532 until the drive belt 404 is tensioned. To tensionthe drive belt 404, a hook, screwdriver, or other tool is inserted intothe grasping slot 542 and the adjustable clamp 536 is pulled outwardrelative to the stationary plate 532 so as to tension the drive belt.The adjustable clamp 536 and the grasping slot 542 are arranged so thatthey can be accessed when the hinged closure panel 42 is open,underneath upper cross member 58 of the rectangular enclosure 24. Oncethe drive belt 404 has sufficient tension, the bolts 544 are tightenedto hold the adjustable clamp 536 into position. In this manner, thedrive belt 404 is tensioned.

Periodically, after several extensions of the ramp platform 28, thedrive belt 404 may be stretched, and may require tightening. To do this,the bolts 544 are loosened, a tool is placed in the grasping slot 542,and the drive belt 404 is tightened. The bolts 544 can then beretightened so as to fix the position of the adjustable clamp 536.

The ramp assembly 300 includes close-out bearings 552 (FIG. 41) formedof a low friction material such as Delrin. The close-out bearings 552perform much of the same function as the V-shaped brackets 44 of theramp assembly 20. However, the close-out bearings 552, because of thelow friction material, do not damage or scratch the ramp platform 28upon extension and retraction of the ramp assembly 300.

A wire rope retainer 560 (FIG. 53) is provided for the pulley 466. Thewire rope retainer 560 is mounted over the pulley 466 so that the pulleyfreely spins therein. The wire rope retainer 560 is a single piece ofmetal that forms a U-bracket 561 that extends around the outside of thepulley 466 and is attached at the axle of the pulley on opposite sidesof the pulley. A flange 562 extends along one side of the pulley 466 offof one side of the U-bracket 561 and upward to form an L-bracket 564that fits around an edge of the pulley 466. The L-bracket 564 and theU-bracket 561 form two retainers for holding the cable 464 on the pulley466.

A second L-bracket 565 extends outward from the flange 562 in oppositedirection of L-bracket 564 and fits into a slot 567 (FIG. 37) of thebottom panel 38 adjacent to the axle 566 for the pulley 466. TheL-bracket 565 prevents rotation of the wire rope retainer 560 when themanual bolt relase mechanism 400 is actuated. The wire rope retainer 560retains the cable 464 on the pulley 466 should cable 464 go slack. Thewire rope retainer 560 can also be used in a similar manner around thepulleys 200 and 202 and cable 184 of manual unlatching mechanism 366 or180.

While the preferred embodiment of the invention has been illustrated anddescribed with reference to preferred embodiments thereof, it will beappreciated that various changes can be made therein without departingfrom the spirit and scope of the invention as defined in the appendedclaims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A ramp assemblycomprising: (a) a frame; (b) a ramp platform mounted in the framedefining trailing and forward ends and extendible and retractable alonga length of the frame between stowed and deployed positions, the rampplatform being arranged when deployed such that the forward end extendsdown toward the ground; (c) a first locking mechanism that locks theramp platform into a fully deployed position, wherein the first lockingmechanism comprises a first latch plate attached to the frame and afirst latch arm operatively associated with the ramp platform to extendand retract with the ramp platform and configured and arranged so as toengage and lock onto the first latch plate when the ramp platform is inthe fully deployed position, wherein the first locking mechanismcomprises a second latch plate attached to the frame and a second latcharm operatively associated with the ramp platform to extend and retractwith the ramp platform and configured and arranged so as to engage andlock onto the second latch plate when the ramp platform is in the fullydeployed position; (d) a second locking mechanism that locks the rampplatform into a fully stowed position; (e) a coupling linking movementof the first and second latch arms; (f) a spring arranged to bias thefirst and second latch arms to engage and lock onto the first and secondlatch plates, respectively; (g) a solenoid actuator operativelyassociated with the second latch arm so that actuation of the solenoidactuator disengages the first and second latch arms from the first andsecond latch plates, respectively, in the fully deployed position, anddisengages the second latch arm from the stowed latch plate in the fullystowed position; (h) a reciprocating mechanism for extending andretracting the ramp platform along a length of the frame between stowedand deployed positions; and (i) a time delay circuit, the time delaycircuit configured to delay the actuation of the reciprocating mechanismuntil after actuation of the solenoid actuator, so that the first andsecond latch arms are fully disengaged from the first and second latchplates, respectively, before actuation of the reciprocating mechanism inthe fully deployed position, and so that the second latch arm is fullydisengaged from the stowed latch plate before actuation of thereciprocating mechanism in the fully stowed position.
 2. The rampassembly of claim 1, wherein the first and second latch plates areadjustable along a longitudinal axis of the frame.
 3. The ramp assemblyof claim 1, wherein the second locking mechanism comprises a stowedlatch plate attached to the frame that is engaged by and locked onto bythe second latch arm when the ramp platform is in the fully stowedposition.
 4. The ramp assembly of claim 1, wherein the time delaycircuit is further configured to simultaneously deactuate the solenoidactuator and actuate the reciprocating mechanism.
 5. A ramp assemblycomprising: (a) a frame; (b) a ramp platform mounted in the framedefining trailing and forward ends and extendible and retractable alonga length of the frame between stowed and deployed positions, the rampplatform being arranged when deployed such that the forward end extendsdown toward the ground; (c) a first locking mechanism that locks theramp platform into a fully deployed position, wherein the first lockingmechanism comprises a first latch plate attached to the frame and afirst latch arm operatively associated with the ramp platform to extendand retract with the ramp platform and configured and arranged so as toengage and lock onto the first latch plate when the ramp platform is inthe fully deployed position; (d) a second locking mechanism that locksthe ramp platform into a fully stowed position, wherein the secondlocking mechanism comprises a stowed latch plate attached to the framethat is engaged by and locked onto by the first latch arm when the rampplatform is in the fully stowed position; (e) a spring arranged to biasthe first latch arm to engage and lock onto the first latch plate; (f) asolenoid actuator operatively associated with the first latch arm sothat actuation of the solenoid actuator disengages the first latch armfrom the first latch plate in the fully deployed position, anddisengages the first latch arm from the stowed latch plate in the fullystowed position; (g) a reciprocating mechanism for extending andretracting the ramp platform along a length of the frame between stowedand deployed positions; and (h) a time delay circuit, the time delaycircuit configured to delay the actuation of the reciprocating mechanismuntil after actuation of the solenoid actuator, so that the first latcharm is fully disengaged from the first latch plate before actuation ofthe reciprocating mechanism in the fully deployed position, and so thatthe first latch arm is fully disengaged from the stowed latch platebefore actuation of the reciprocating mechanism in the fully stowedposition.
 6. The ramp assembly of claim 5, wherein the time delaycircuit is further configured to simultaneously deactuate the solenoidactuator and actuate the reciprocating mechanism.
 7. The ramp assemblyof claim 5, further comprising a single manual release mechanism,actuation of which (1) releases the first locking mechanism when theramp assembly is in the fully deployed position and (2) releases thesecond locking mechanism when the ramp platform is in the fully stowedposition.
 8. The ramp assembly of claim 7, wherein the first latch plateis adjustable along the longitudinal axis of the frame.
 9. The rampassembly of claim 7, wherein the second latch plate is adjustable alonga longitudinal axis of the frame.
 10. The ramp assembly of claim 5,wherein the first locking mechanism comprises a second latch plateattached to the frame and a second latch arm operatively associated withthe ramp platform to extend and retract with the ramp platform andconfigured and arranged so as to engage and lock onto the second latchplate when the ramp platform is in the fully deployed position.
 11. Theramp assembly of claim 10, further comprising a coupling linkingmovement of the first and second latch arms.
 12. The ramp assembly ofclaim 11, wherein the single manual release mechanism comprises a handle(1) operatively associated with the first latch arm when the rampplatform is in the deployed position such that actuation of the handlecauses the first and second latch arms to release the first and secondlatch plates, and (2) operatively associated with the first latch armwhen the ramp platform is in the stowed position such that actuation ofthe handle causes the second latch arm to release the stowed latchplate.
 13. A ramp assembly comprising: (a) a frame; (b) a ramp platformmounted in the frame defining trailing and forward ends and extendibleand retractable along a length of the frame between stowed and deployedpositions, the ramp platform being arranged when deployed such that theforward end extends down toward the ground; (c) a first lockingmechanism that locks the ramp platform into a fully deployed position,wherein the first locking mechanism comprises a first latch plateattached to the frame and a first latch arm operatively associated withthe ramp platform to extend and retract with the ramp platform andconfigured and arranged so as to engage and lock onto the first latchplate when the ramp platform is in the fully deployed position; (d) asecond locking mechanism that locks the ramp platform into a fullystowed position, wherein the second locking mechanism comprises a stowedlatch plate attached to the frame that is engaged by and locked onto bya second latch arm when the ramp platform is in the fully stowedposition; (e) a solenoid actuator operatively associated with the firstand second latch arms so that actuation of the solenoid actuatordisengages the first latch arm from the first latch plate in the fullydeployed position, and disengages the second latch arm from the stowedlatch plate in the fully stowed position; (f) a reciprocating mechanismfor extending and retracting the ramp platform along a length of theframe between stowed and deployed positions; and (g) a time delaycircuit, the time delay circuit configured to delay the actuation of thereciprocating mechanism until after actuation of the solenoid actuator,so that the first latch arm is fully disengaged from the first latchplate before actuation of the reciprocating mechanism in the fullydeployed position, and so that the second latch arm is fully disengagedfrom the stowed latch plate before actuation of the reciprocatingmechanism in the fully stowed position.
 14. The ramp assembly of claim13, wherein the time delay circuit is further configured tosimultaneously deactuate the solenoid actuator and actuate thereciprocating mechanism.